Focused charged particle beams are used in many fields including scanning electron and ion microscopy and lithography. The size, shape, and distribution of such charged particle beams, referred to as the point spread function (PSF), is critically important. For example, in the case of a scanning electron microscope (SEM), it is a limiting factor in determining spatial resolution and is also an indicator of instrument performance. Because the beams involved are so small (often from 1 to 20 nanometers at the sample plane) there is no direct detector that can measure the PSF. Without the ability to directly measure the PSF of the charged particle beam, the PSF must be calculated and then may be used to restore images to have higher image resolution, clarity, and/or quality for subsequent examination and analysis. Computational methods for PSF determination are emerging, however, these computational methods are extremely complex, and time consuming. As a result, leave many opportunities for error in the computation.